Question

I have

data Dictionary a = Empty
                  | Branch (a, Bool, Dictionary a) (Dictionary a)
                  deriving (Ord, Eq)

instance Show (Dictionary a) where show = showDict

showDict (Branch (val, e, dict) dict2) = "My dict is : " ++ val 

I know it is definitely wrong but I could not find how to write this one. In showDict function type of val is a but expected type is [Char].

Thanks in advance.

Answer 1

To turn val into a string, show it:

showDict (Branch (val, e, dict) dict2) = "My dict is : " ++ show val

And don’t forget the type constraints on showDict:

instance Show a => Show (Dictionary a) where show = showDict